<?php

// 应用公共文件
/**
 *  * 字符串截取，支持中文和其他编码
 * static
 * access public
 * @param $str 需要转换的字符串
 * @param int $start 开始位置
 * @param $length 截取长度
 * @param string $charset 编码格式
 * @param bool $suffix 截断显示字符
 * @return string
 */
function msubstr($str, $start=0, $length, $charset="utf-8", $suffix=true) {
    if(function_exists("mb_substr")){
        $slice = mb_substr($str, $start, $length, $charset);
        $strlen = mb_strlen($str,$charset);
    }elseif(function_exists('iconv_substr')){
        $slice = iconv_substr($str,$start,$length,$charset);
        $strlen = iconv_strlen($str,$charset);
    }else{
        $re['utf-8']   = "/[\x01-\x7f]|[\xc2-\xdf][\x80-\xbf]|[\xe0-\xef][\x80-\xbf]{2}|[\xf0-\xff][\x80-\xbf]{3}/";
        $re['gb2312'] = "/[\x01-\x7f]|[\xb0-\xf7][\xa0-\xfe]/";
        $re['gbk']    = "/[\x01-\x7f]|[\x81-\xfe][\x40-\xfe]/";
        $re['big5']   = "/[\x01-\x7f]|[\x81-\xfe]([\x40-\x7e]|\xa1-\xfe])/";
        preg_match_all($re[$charset], $str, $match);
        $slice = join("",array_slice($match[0], $start, $length));
        $strlen = count($match[0]);
    }
    if($suffix && $strlen>$length)$slice.='...';
    return $slice;
}

/**
 * 默认生成6位随机字符串
 * @param int $length
 * @return string
 */
function strss($length = 6) {
    if (!is_int($length) || $length <= 0) return false;
    $str = '1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ~!@#$%^&*()_+|-=';
    $substr = '';
    for ($i = 0; $i< $length; $i++) {
        $substr .= $str[mt_rand(0, strlen($str) - 1)];
    }
    return $substr;
}

/**
 * 格式化字节大小
 * @param  number $size      字节数
 * @param  string $delimiter 数字和单位分隔符
 * @return string            格式化后的带单位的大小
 */
function format_bytes($size, $delimiter = '') {
    $units = array('B', 'KB', 'MB', 'GB', 'TB', 'PB');
    for ($i = 0; $size >= 1024 && $i < 5; $i++) $size /= 1024;
    return round($size, 2) . $delimiter . $units[$i];
}